In the art of commercial airplanes, it is highly desirable to design airplane and engine configurations that yield reduced fuel burn to increase efficiency and lower cost. In addition, carbon trading regulations comparable to those already enacted in the European Union may also likely to be adopted in other industrialized nations including the United States. These environmental considerations become even more important in economic scenarios in which fuel cost increases. This motivates a need for step-change technologies to reduce fuel consumption.
Conventional military cargo airplane configurations address two disparate missions: devise a military cargo airplane that provides more fuel-efficient transport of cargo in typical operations; and provide a means to load large wheeled vehicles into the airplane without the use of ground-based equipment. In general, these airplanes have a requirement to carry a large, dense and heavy payload. For example, an existing cargo plane can carry a main battle tank that weighs about 160,000 lb and has floor space to carry 18 cargo pallets. These pallets typically have a weight limit of about 10,000 lb each, but in actual service are typically loaded with a weight of about 5000 lb each for a typical payload weight of about 90,000 lb. This means that the existing cargo plane may not have sufficient floor area (or payload volume) to carry a pallet payload weight approaching the airplane's actual capacity. Therefore, it may be typical that too much airplane is used to fly too little payload, resulting in a relatively large fuel burn per unit of payload. A typical metric of airplane fuel efficiency and carbon dioxide emissions is payload multiplied by range divided by fuel burned (ton-miles per pound of fuel). A way to address these challenges is to take advantage of the inherent fuel efficiency of a blended wing body (BWB) configuration.
A BWB is an airframe design that incorporates design features from both traditional fuselage and wing design, and flying wing design. Advantages of the BWB approach include efficient high-lift wings and a wide airfoil-shaped body. BWB aircraft have a flattened and airfoil shaped body (i.e., relative to a conventional aircraft), which produces lift (i.e., in addition to wing lift) to keep itself aloft. Flying wing designs comprise a continuous wing incorporating the functions of a fuselage in the continuous wing. Unlike a flying wing, the BWB has wing structures that are distinct and separate from the fuselage, although the wings are smoothly blended with the body. The efficient high-lift wings and wide airfoil-shaped body enable the entire craft to contribute to lift generation with the resultant potential increase in fuel economy.
BWB freighter designs are not currently being manufactured. Of the existing designs, most use large cargo doors in the centerbody leading edge. The chief disadvantage and limitation of this arrangement is that rolling stock can only be loaded with extensive ground-based cargo handling equipment. It would be preferable to have a rear (aft) cargo ramp in order to load large wheeled vehicles that can drive up the ramp. Existing BWB designs lack an airframe design that can incorporate a rear cargo door and ramp into the BWB configuration without disrupting aerodynamic performance. Integration of a rear cargo door and ramp into a BWB configuration may require preserving favorable lift distribution, avoiding separation of airflow over the BWB, and preserving pitch trim stability and control capability.
Thus, there is a need for a rear (aft) cargo door and ramp access for blended wing body airframes that does not reduce aerodynamic performance, stability, and control capability.